Feizhou a écrit :
If it is a phpbb bug, is there an easy way to have a fake smtp server, so I can catch the bugged phpbb smtp request? (I can setup another smtp port in phpbb...)
smtp-sink is a program that comes with postfix that sends all mails it receives to Dave Null. You can tell it to log smtp commands to syslog or display smtp conversations on screen or redirect them to a file. man smtp-sink for more information. You can also run this on any port on localhost as you fancy to test out another instance of your current phpbb.
Thanks for your suggestion. I tried smtp-sink on another port and found that phpbb was the cause of the problem. phpbb did several connections to the smtp-sink and sent multiple emails with more than 50000 recipients instead of 3500. When I sorted the smtp-sink output, I could see recipients duplicated multiple times.
Conclusion postfix works great! phpbb sucks!
Thank you all for your support.